וְהָיָה֩ בֵית־יַעֲקֹ֨ב אֵ֜שׁ וּבֵ֧ית יוֹסֵ֣ף לֶהָבָ֗ה וּבֵ֤ית עֵשָׂו֙ לְקַ֔שׁ וְדָלְק֥וּ בָהֶ֖ם וַאֲכָל֑וּם וְלֹֽא־יִֽהְיֶ֤ה שָׂרִיד֙ לְבֵ֣ית עֵשָׂ֔ו כִּ֥י יְהוָ֖ה דִּבֵּֽר׃
Rashi on Obadiah
for the Lord has spoken—Now where did He speak? (Num. 24:19) “Out of Jacob shall come a ruler, and he shall destroy him that remains in the city.” [from Mechilta Bo 12:16, Pirk&d’Rabbi Eliezer ch. 37]